Low QRS Voltage

Diagnostic criteria

---

Mechanisms

Low voltage is produced by:

• The “damping” effect of increased layers of fluid, fat or air between the heart and the recording electrode
• Loss of viable myocardium
• Diffuse infiltration or myxoedematous involvement of the heart

Causes

The most important cause is massive pericardial effusion, which produces a triad of:

• Low voltage
• Tachycardia
• Electrical alternans

Patients with this triad need to be immediately assessed for clinical or echocardiographic evidence of tamponade.

Other causes of low voltage include:

---

ECG Examples

Example 1

Massive Pericardial Effusion:

---

Example 2

Prior Massive Anterior MI:

• Low QRS voltage in V1-6. This diffuse loss of R wave height suggests extensive myocardial loss from a prior anterior MI.
• There is also biphasic anterior T waves (Wellens syndrome) indicating new critical occlusion of the LAD artery

---

Example 3

Emphysema:

• Low voltages in the limb leads is classically seen in patients with emphysema.
• Other assocaited ECG features of emphysema include:
  • Right axis deivation
  • Peaked P waves (P pulmonale)
  • Clockwise rotation (persistent S wave in V6)

---

---

References

---

Advanced Reading

Online

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

---

LITFL Further Reading

---